1. Field of the Invention
The invention generally relates to a signal receiving technique, and more particularly, to a signal receiving device which analyzes an input signal and automatically adjusts the input impedance of the input signal and an electronic apparatus using the same.
2. Description of Related Art
Conventionally, a signal buffer is usually disposed at the signal input terminal of an electronic apparatus. This signal buffer allows an input signal to maintain a reasonable voltage level before the input signal is sent to a signal processing unit (for example, a processing chip) in the electronic apparatus. Or, a rated input resistor is disposed at the signal input terminal of the electronic apparatus according to the standard specification of the input signal.
However, in an existing electronic apparatus, the signal buffer may be removed or the impedance of the input resistor may be changed due to the updated fabrication process and the consideration of the fabrication cost. When the signal buffer is removed, the impedance of the input resistor is changed, or the signal input terminal of the electronic apparatus cannot predict too large or too small amplitude of the input signal, the electronic apparatus can only calibrate the input signal to avoid any distortion of the input signal through the gain control function and the signal clamping function of the signal processing unit.
Below, the situation mentioned above will be explained with an example. FIG. 1 is a diagram of a general image application system 100 (for example, a television signal sharing application or a monitor controlling application adopting image transmitting/processing techniques). In the image application system 100 in FIG. 1, in order to allow multiple electronic apparatuses 110 (for example, televisions) to obtain the same input signal 130 (for example, an image signal) at the same time, the signal input terminals 115 of the electronic apparatuses 110 are connected with each other in parallel and are electrically connected to the same image signal source 120. When the amplitude of the input signal 130 is too small, the electronic apparatuses 110 can amplify the input signal 130 through the gain control function of the signal processing unit 140 (for example, a image processing chip) to resolve aforementioned problem.
However, when the signal input terminals 115 of the electronic apparatuses 110 are connected with each other in parallel, the impedance of the rated input resistor RR of each electronic apparatus 110 attenuates drastically. In some techniques, the input resistors RR are removed to avoid the signal attenuation problem. However, through such a technique, the amplitude of the input signal 130 is amplified several times. If the amplitude of the input signal 130 is too large and exceeds a limited input range of the signal processing unit 140 (assumed to be the voltage input range of the signal processing unit 140, namely, the peak-to-peak voltage (upper limit) of the input signal should not exceed 1.5V), the portion of the input signal 130 exceeding the limited input range (1.5V) is clamped and discard. Because the signal processing unit 140 cannot obtain the discarded portion of the input signal 130 during the backend processing, the input signal 130 is distorted.
Thereby, how to allow the electronic apparatus to receive a lossless input signal when aforementioned problems exist is a major subject in existing signal transmitting/processing techniques.